Bornyl and isobornyl esters of carboxylic acids of condensed tetrahydroquinoxalines

ABSTRACT

Bornyl and isobornyl esters of carboxylic acids of condensed tetrahydroquinoxalines having the general formula ##STR1## where R 1  is CH 3  or C 2  H 5  ##STR2## where R 2  is ##STR3## The proposed compounds are active against viruses and can therefore be used in medicine.

FIELD OF THE ART

This invention relates to organic chemistry, and more particularly it relates to new compounds, bornyl and isobornyl esters of carboxylic acids of condensed tetrahydroquinoxalines having antiviral properties.

PRIOR ART

Known in the prior art are derivatives of 3a, 4, 9,9a-tetrahydrofuro (2,3a-b) quinoxaline (O. N. Chupakhin, V. N. Charushin, A. I. Chernyshev, "Application of ¹ H, ¹³ C and ¹⁵ N NMR in the Chemistry of 1,4-Diazines", Progress in Nuclear Magnetic Resonance Spectroscopy, Oxford; Pergamon Press, 1988, vol. 20 (2), pp. 177-184. However, the compound are not effective against viruses.

DISCLOSURE OF THE INVENTION

The proposed compounds are novel and have not been described in the literature.

The object of the invention is to provide new compounds having high antiviral activity and low toxicity.

The object is accomplished by provision of new compounds, which, according to the invention, are bornyl and isobornyl esters of carboxylic acids of condensed tetrahydroquinoxalines of the general formula: ##STR4## where: R¹ =CH₃ ; C₂ H₅ ; ##STR5##

The proposed compounds have low toxicity and are active against influenza virus A and B. The most active compound, according to the invention, is isobornyl ester of 2,9-dimethyl-3a,4,9,9a-tetrahydrofuro 2,3-b quinoxaline-3-carboxylic acid of the formula ##STR6##

Said compound has a broad spectrum of antiviral activity, i.e., it is highly active against tick-borne encephalitis virus, epidemic strains of influenza virus A, B and C resistant to remantadine, and also against the agent causing respiratory syncytial infection.

Best Mode of Carrying Out the Invention

The proposed new compounds-bornyl and isobornyl esters of carboxylic acid of condensed tetrahydroquinoxalines are colorless crystals readily soluble in chloroform and dimethylsulphoxide, moderately soluble in ethyl ether and ethyl alcohol, and sparingly soluble in water.

The structure of the proposed compounds was confirmed by the findings of elemental analysis and ¹ H NMR spectroscopy. The proposed compounds are active against viruses. The antiviral activity of the proposed compounds was studied on experimental animals.

The activity of the proposed compounds against influenza virus A and B was tested. The following compounds were tested:

isobornyl ester of 2,9-dimethyl-3a,4,9,9a-tetrahydrofuro 2,3-b quinoxaline-3-carboxylic acid (compound 1a);

isobornyl ester of 2-methyl-9-ethyl-3a,4,9,9a-tetrahydrofuro [2,3-b] quinoxaline-3-carboxylic acid (compound 1b);

bornyl ester of 2-methyl-9-ethyl-3a,4,9,9a-tetrahydrofuro [2,3-b] quinozaline-3-carboxylic acid (compound 1c);

bornyl ester of 3a,5-dimethyl-2-phenyl-3a,4, 4a,5,10,10a-hexahydro-1,3,4-thiadiazole [2,3-a] quinoxaline (2,3-d) pyrrole-4carboxylic acid (compound 1d);

isobornyl ester of 3a,5-dimethyl-2-phenyl-3a,4, 4a,5,10,10a-hexahydro-1,3,4-thiadiazole [2,3-a] quinoxaline [2,3-d]-pyrrole-4-carboxylic acid (compound 1e).

The proposed compounds were compared with the known antivirus drugs remantadine and adapromine.

The antiviral activity of the compounds was studied on chick embryos and albino mice infected with the virus.

The studies and estimation of efficacy of the compounds were performed according to the known procedure.

Experiments were carried out on 3 groups of animals (or embryos): test group (the virus and the proposed compounds were given), control group (the virus and distilled water or a 0.9% sodium chloride solution were given) and the group for comparison (the virus and the known antiviral compounds remantadine or adapromine were given).

The virus was given intransally to mice under a mild ether anaesthesia. The antiviral compounds were given per os a in dose of 1 mg per animal.

The results of the test are given in Tables 1 through 5.

                                      TABLE 1                                      __________________________________________________________________________     Studies on the Antiviral Activity of the Proposed Compound 1a in               Experiments                                                                    on Mice Infected with Influenza Virus A and B Compared with the Known          Drugs Remantadine, Adapromine and Control.                                              Mice infected with influenza virus                                             influenza virus A                                                                               influenza virus B                                             compound         compound                                             Indices  1a    remantadine                                                                           control                                                                            1a    adapromine                                                                           control                                  1        2     3      4   5     6     7                                        __________________________________________________________________________     % of diseased                                                                           27    13     77  20    20    74                                       mice and of                                                                    died mice                                                                      Factor of                                                                               2.8   6.0    --  3.7   3.7   --                                       reduction of                                                                   number of                                                                      diseased mice                                                                  (protection                                                                    factor)                                                                        Efficiency, %                                                                           64    83     --  73    73    --                                       Activity of                                                                             +++   ++++   --  +++   +++   --                                       compound                                                                       Mean incubation                                                                         9.7   10.0   8.0 11.0  10.9  8.6                                      period, days                                                                   Elongation of                                                                           1.6   2.8    --  2.4   2.3   --                                       animals life in                                                                test group com-                                                                pared with con-                                                                trol, days                                                                     __________________________________________________________________________

                                      TABLE 2                                      __________________________________________________________________________     Studies on Antiviral Activity of Compound 1b in Experiments on Mice            Infected with Influenza virus A and B (Compared with the Known                 Drugs Remantadine, Adapromine and Control)                                              Mice infected with influenza virus A and B                                     influenza virus A                                                                               influenza virus B                                             compound         compuond                                             Indices  1b    remantadine                                                                           control                                                                            1b    adapromine                                                                           control                                  1        2     3      4   5     6     7                                        __________________________________________________________________________     % of diseased                                                                           47    5      73  27    20    75                                       mice and of                                                                    died mice                                                                      Factor of                                                                               1.6   14.6   --  2.9   3.8   --                                       reduction of                                                                   number of                                                                      diseased mice                                                                  (protection                                                                    factor)                                                                        Efficiency, %                                                                           37    93     --  65    74    --                                       Activity of                                                                             +     ++++   --  +++   +++   --                                       compound                                                                       Mean incubation                                                                         9.2   11.7   7.7 10.0  10.3  7.9                                      period, days                                                                   Elongation of                                                                           2.1   4.0    --  2.2   2.4   --                                       animals life                                                                   in test group                                                                  compared with                                                                  control, days                                                                  __________________________________________________________________________

                                      TABLE 3                                      __________________________________________________________________________     Studies of Antiviral Activity of the Proposed Compound 1c in Experiments       on                                                                             Mice Infected with Influenza Virus A and B (Compared with the Known            Drugs Remantadine and Adapromine, and Control)                                          Mice infected with influenza virus A and B                                     influenza virus A                                                                               influenza virus B                                             compound         compound                                             Indices  1c    remantadine                                                                           control                                                                            1c    adapromine                                                                           control                                  1        2     3      4   5     6     7                                        __________________________________________________________________________     % of diseased                                                                           43    15     69  25    25    70                                       mice and of                                                                    died mice                                                                      Factor of                                                                               1.6   14.6   --  2.8   2.8   --                                       reduction of                                                                   number of                                                                      diseased mice                                                                  (protection                                                                    factor)                                                                        Efficiency, %                                                                           37    85     --  64    64    --                                       Activity of                                                                             +     ++++   --  +++   +++   --                                       compound                                                                       Mean incubation                                                                         10.0  11.7   9.0 11.0  11.1  8.6                                      period, days                                                                   Elongation of                                                                           1.0   2.7    --  2.4   2.5   --                                       animals life                                                                   in test group                                                                  compared with                                                                  control, days                                                                  __________________________________________________________________________

                  TABLE 4                                                          ______________________________________                                         Studies on Antiviral Activity of Compounds 1d and 1e in                        Experiments on Mice Infected with Influenza Virus B                            (Compared with Adapromine and Control)                                                   Mice infected with influenza virus B                                             proposed compound                                                  Indices     1d       1e        adapromine                                                                             control                                 1           2        3         4       5                                       ______________________________________                                         % of diseases mice                                                                         20       21        12      72                                      and died mice                                                                  Factor of   3.6      3.4       6.0     --                                      reduction of                                                                   number of diseased                                                             mice (protection                                                               factor)                                                                        Efficiency, %                                                                              72       71        83      --                                      Activity of +++      +++       ++++    --                                      compounds                                                                      Mean incubation                                                                            11.0     10.9      11.6    --                                      period, days                                                                   Elongation of                                                                              2.5      2.4       3.1     --                                      animals life in                                                                test group, days                                                               ______________________________________                                    

                  TABLE 5                                                          ______________________________________                                         Results of Studies on Antiviral Activity of Proposed                           Compounds 1a through 1e in Experiments on Mice Infected                        with Influenza Virus A and B                                                            Influenza virus A                                                                           Influenza virus B                                                       Efficiency,      Efficiency,                                    Nos  Compound  %         Activity                                                                              %       Activity                               1    2         3         4      5       6                                      ______________________________________                                         1.   Proposed  64        +++    73      +++                                         compound                                                                       1a                                                                        2.   Proposed  37        +      65      +++                                         compound                                                                       1b                                                                        3.   Proposed  37        +      64      +++                                         compound                                                                       1c                                                                        4.   Proposed  --               72      +++                                         compound                                                                       1d                                                                        5.   Proposed  --               71      +++                                         compound                                                                       1e                                                                        ______________________________________                                    

It can be seen from the Tables 1 through 5 that all proposed compounds are active against influenza virus B. The proposed compounds 1a through 1c are also active against influenza virus A. Compound 1a is especially effective (isobornyl ester of 2,9-dimethyl-3a,4,9a-tetrahydrofuro[2,3-d]quinozaline-3-carboxylic acid). The antiviral properties of compound 1a were studied in detail.

It was shown in experiments on chick embryos and albino mice that compound 1a has marked antiviral activity, it inhibits reproduction of influenza virus types A and B and saves mice infected with the virus.

The results of the tests are given in Tables 6 and 7.

                                      TABLE 6                                      __________________________________________________________________________     Results of Testing Antiviral Activity of Compound 1a in                        Experiments on Mice Infected with Influenza Virus A and B                      (the drug was given to mice in a dose of 1 mg/mouse, 24 hours and              1 hour before infection and in 24, 48 and 72 hours after infection)                       Mice infected with influenza virus                                             influenza virus A                                                                               Influenza virus B                                             compound         compound                                           Indices    1a    remantadine                                                                           control                                                                            1a    remantadine                                                                           control                               1          2     3      4   5     6      7                                     __________________________________________________________________________     % of diseased                                                                             27    13     77  20    20     74                                    mice and died                                                                  mice                                                                           Protection 2.8   6.0    --  3.7   3.7    --                                    factor                                                                         Efficiency, %                                                                             64    83     --  73    73     --                                    Activity   +++   ++++   --  +++   +++    --                                    Mean Incubation                                                                           9.7   10.0   8.0 11.0  10.9   8.6                                   Elongation of animal                                                                      1.6   2.8    --  2.4   2.3    --                                    life in test group                                                             (compared with                                                                 control), day                                                                  __________________________________________________________________________

It can be seen from Table 6 that the activity of compound 1a is sufficiently high and commensurable with that of remantadine and adapromine (remantadine and adapromine are the most active known anti-influenza drugs).

Lower activity of the proposed drug 1a against influenza virus A compared with remantadine can probably be compensated by enlargement of the dose because the toxicity of the proposed drug is 2.5-3 times lower than that of remantadine (see Table 7).

                                      TABLE 7                                      __________________________________________________________________________     Chemotherapeutic Index of Compound 1a Compared with                            that of Remantadine and Adapromine                                                              Minimum effective                                                                          Chemotherapeutic                                            Toxicity                                                                              dose (mg/mouse)                                                                            index for influenza                                         for mice                                                                              against influenza viruses                                                                  viruses                                           Nos                                                                               Drug   (mg/mouse)                                                                            type A                                                                               type B                                                                               type A                                                                              type B                                       1  2      3      4     5     6    7                                            __________________________________________________________________________     1. Proposed                                                                              16     0.2   0.04  80   400                                             compound 1a                                                                 2. Remantadine                                                                           6      0.1   --    60   --                                           3. Adapromine                                                                            6      --    1.0   --    6                                           __________________________________________________________________________

Table 7 shows that compound 1a has very high chemotherapeutic index for influenza virus A (about 80) and virus B (about 400) which is substantially higher than those of remantadine and adapromine.

The efficiency of compound against influenza viruses A and B is 60-70%. The compound is effective as a preventive means as well when administered 24 and 1 hour before infection or given in 24, 48 and 72 hours after infection. It is also effective as a therapeutic means.

The activity of the proposed compound 1a against influenza virus C has been studied. Experiments were performed on chick embryos because this virus does not propagate in the lungs of mice. The results are given in Table 8. They show that the compound inhibits reproduction of influenza virus C.

                  TABLE 8                                                          ______________________________________                                         Results of Testing Antiviral Activity of proposed                              Compound 1a in Experiments on Chick Embryos Infected                           with Influenza Virus C                                                                    Titre of virus (lg) in                                                                         Inhibition                                                     embryo treated with                                                                            of virus                                            Influenza virus C        solvent   reproduc-                                   strains      compound 1a (control) tion (lg)                                   1            2           3         4                                           ______________________________________                                         C(USA)1233/47                                                                               2.8 ± 0.4                                                                               4.5 ± 0.3                                                                             1.7                                         C(Leningrad)412/83                                                                          3.5 ± 0.3                                                                               5.0 ± 0.3                                                                             1.5                                         C(Ulan-Ude)131/86                                                                           3.6 ± 0.3                                                                               5.2 ± 0.4                                                                             1.6                                         C(Leningrad)393/87                                                                          3.2 ± 0.3                                                                               4.5 ± 0.3                                                                             1.3                                         ______________________________________                                    

The effect of the proposed compound 1a on morbidity and mortality of young mice borne from females infected with the virus was studied.

It was shown that the proposed compound 1a given to pregnant or nursing mice protects the sucklings from trasnplacental infection with the virus or infection from a diseased mouse.

The results of the test are given in Tables 9, 10 and 11.

Table 9 shows the results of the experiment where the activity of the proposed compound was estimated by mortality rate. Table 10 shows that the administration of the proposed compound 1a to infected mice protects their nurslings from infection and death; moreover, it promotes their normal growth as estimated by gain in weight. Table 10 shows that the weight of sucklings borne from infected female mice, which were given compound 1a, almost does not differ from the weight of young mice borne from control mice. Administration of compound 1a promotes an asymptomatic course of infection in pregnant mice and formation of immunity in their posterity that protects them from influenza during the first days of life.

Table 11 gives the results of the experiment in which neonate mice borne from infected females were infected with the influenza virus. It can be seen from the Table that the mortality in the control group of young mice (borne from mice infected with the virus without administration of drugs) was much higher than among the mice borne from the animals to whom the virus and the proposed compound 1a were given.

                  TABLE 9                                                          ______________________________________                                         Mortality of Mice Borne from Infected Females                                             % of lethal cases among mice                                                   after infection of their mothers                                    Compound given to                                                                           in 6    in 7    in 8  in 9  in 10                                 female mice  days    days    days  days  days                                  1            2       3       4     5     6                                     ______________________________________                                         Compound 1a + virus                                                                          3      10      10    10     13                                   placebo + virus                                                                             21      50      68    76    1000                                  ______________________________________                                    

                  TABLE 10                                                         ______________________________________                                         Growth of Mice Borne from Females Infected                                     with Influenza Virus                                                                          Mean weight of suckling mice,                                   Compound given g days                                                          to mice        0      3      5    7    9                                       1              2      3      4    5    6                                       ______________________________________                                         Control        1.5    2.5    2.9  4.0  4.6                                     Proposed compound 1a                                                                          1.5    2.6    3.4  3.4  3.6                                     plus influenza virus                                                           9% sodium chloride                                                                            1.3    1.5    1.5  1.3  all mice                                solution + virus                       died                                    ______________________________________                                    

                  TABLE 11                                                         ______________________________________                                         Effect of Influenza Infection in Pregnant Mice Treated                         with Compound 1a (intranasally) on Sensitivity of                              Neonates to a Lethal Dose of Influenza Virus                                                     Mortality rate amoung                                                          suckling mice, %                                             Compound given to days after infection                                         pregnant mice     4     7        8    11                                       1                 2     3        4    5                                        ______________________________________                                         Proposed compound 1a +                                                                            0     7        23   23                                      influenza virus                                                                9% sodium chloride                                                                               44    88       100  100                                      solution + virus                                                               ______________________________________                                    

The sensitivity to the proposed compound 1a of influenza virus strains resistant to remantadine was studied. The experiments were carried out on chick embryos that were infected into the chorionallantois.

Remantadine and the proposed compound 1a were given in a dose of 1 mg/embryo.

The embryos infected with influenza virus A were incubated for 48 hours at a temperature of 34° C. The presence of the virus in the embryo was determined by inhibition of haemaglutination. The virus titres were counted by Read and Mench. For estimation of the sensitivity of influenza virus strains to the studied compounds, the titre difference was determined (in units of EID₅₀, embryo intective dose) in controls and test embryos. Some virus strains that are resistant or only slightly sensitive to remantadine were sensitive to the proposed compound 1a. The results of the tests are given in Tables 12 and 13.

                  TABLE 12                                                         ______________________________________                                         Studies on Sensitivity of Influenza Virus A to                                 Remantadine and Proposed Compound 1a (in a dose                                of 1 mg/embryo)                                                                                       Titre difference in                                             Virus titres   control and experi-                                             (lg EID.sub.50)                                                                               ment (lg EID.sub.50)                                                                           proposed                                Influenza virus                                                                          con-   reman-  proposed                                                                               reman-                                                                               compound                                A strains trol   tadine  compound                                                                               tadine                                                                               1a                                      1         2      3       4       5     6                                       ______________________________________                                         A(Moscow) 8.0    6.75    4.5     1.25  3.5                                     2848/86/H3N2/                                                                  A(Moscow) 7.25   5.5     4.75    1.75  2.5                                     2813/86/H3N2/                                                                  A(Riga)   6.0    4.75    4.5     1.25  1.5                                     9951/86/H3N2/                                                                  A(Moscow) 8.2    7.5     4.0     0.7   4.2                                     2878/86/H3N2/                                                                  A(Leningrad)                                                                             4.75   4.5     3.0     0.25  1.75                                    23/81/HON1/                                                                    A(Victoria)                                                                              6.25   6.0     4.0     0.25  2.25                                    35/72/H3N2/                                                                    ______________________________________                                    

                  TABLE 13                                                         ______________________________________                                         Studies on Antiviral Activity of Proposed Compound 1a                          in Experiments on Chick Embryos Infected with                                  Influenza Virus A Strains Resistant to Remantadine                                            substance given                                                                      proposed   reman-                                                                               solvent                                  Strain    Index      compound 1a                                                                               tadine                                                                               (control)                                1         2          3          4     5                                        ______________________________________                                         A(Leningrad)                                                                             % of embryos                                                                              0          57.1  62.5                                     23/81/HON1/                                                                              with virus                                                                     efficiency, %                                                                             90         0     --                                                 activity   ++++                                                      A(Victoria)                                                                              % of embryos                                                                              16.6       72.7  91.6                                     35/73/H3N2/                                                                              with virus                                                                     efficiency, %                                                                             84         20    --                                                 activity   ++++                                                      A(Moscow) % of embryos                                                                              0          66.7  88.9                                     2879/86/H3N2/                                                                            with virus                                                                     efficiency, %                                                                             90         24    --                                                 activity   ++++                                                      ______________________________________                                    

Activity of the proposed compound 1a to the agent causing respiratory syncytial infection was tested. In experiments on tissue culture L-41 the proposed compound inhibits reproduction of RS virus (strain Novoshakhtinsky 3030). When given intranasally to infected cotton rats the proposed compound decreases the virus reproduction in the lungs of the animals; the man titre of the virus in the treated rats was 1.8-2.0 lg lower than in control group of animals. The results of the experiment are illustrated in Table 14.

                  TABLE 14                                                         ______________________________________                                         Effect of Proposed Compound 1a on Reproduction of RS                           Virus (strain Novoshakhtinsky 3080)                                            in L-41 Tissue Culture                                                                        Substance added to tissue                                                      culture                                                                                     0.9% NACl                                          Indices          compound 1a                                                                               solution                                           1                2          3                                                  ______________________________________                                         % of test tubes with                                                                            17         90                                                 degenerated culture                                                            Intensity of reduction                                                                          0.18       2.2                                                of quantity of test                                                            tubes with degenerated                                                         cultures                                                                       Factor of reduction                                                                             5.3                                                           of quantity of test                                                            tubes with degenerated                                                         cultures                                                                       Efficiency, %    81                                                            Activity         ++++                                                          ______________________________________                                    

The studies of the compound 1a revealed antiviral activity of the compound against the causative agent of tick-borne encephalitis.

Experiments were carried out on mongrel albino mice weighing 16-18 g.

The mice divided into two groups, the test and the control one, each of 15 mice. The virus of tick-borne encephalitis (Absettar strain) was given subcutaneously to the animals in both groups. 4 hours before infection, and also in 24, 48, 72 and 96 hours after infection, the animals in the test group were given 0.2 ml of a 0.5% solution of compound 1a in a 0.9% NaCl solution, with an additive of Tween-80 (into the stomach through a gastric tube). The mice in the control group were given 0.2 ml of the 0.9% aqueous solution of sodium chloride.

The mortality of mice in both groups was studied until the animals stopped dying.

The results of the experiments are given in Table 15. They show that the mortality rate decreases significantly if the mice were treated with the proposed compound 1a (from 62.5% in the control group to 18.7% in the test group, i.e. 3.3 times less). Thus, the proposed compound 1a is highly active against the causative agent of tick-borne encephalitis.

                  TABLE 15                                                         ______________________________________                                         Studies on Antiviral Activity of Proposed Compound 1a                          in Experiments on Mice Infected with tick borne                                Encephalitis Virus (Absettar strain)                                                          Substance given to mice                                                                      Physiological                                                                  saline solution                                   Indices          Compound 1a (control)                                         ______________________________________                                         % of diseased mice and                                                                          18.7        62.5                                              mice which died                                                                Factor of reduction of                                                                          3.3         --                                                quantity of diseased                                                           mice (protective factor)                                                       Efficiency, %    70          --                                                Activity of compound 1a                                                                         ++++        --                                                Mean incubation period,                                                                         11.4         9.9                                              days                                                                           Elongation of animal life in                                                                    1.5         --                                                group of treated animals, days                                                 ______________________________________                                    

Acute toxicity of the proposed compounds 1a through 1e was tested in experiments on mongrel albino mice with oral administration of the drug. The compounds given in doses from 800 to 2000 mg/kg of body weight weight did not cause death. The LD₅₀ of remantadine was 640 mg/kg, and that of adapramine, 45 mg/kg.

The proposed compounds were tested for their effect on the mutagenic activity. The results of the tests showed the absence of mutagenic activity in the proposed compounds.

Thus, the experiments show that the proposed compounds have low toxicity and they are active against influenza virus A and B. The compound 1a has the most pronounced effect against the virus of the tick-borne encephalitis, epidemic, influenza viruses A, B and C, including those resistant to remantadine, and also the virus causing respiratory syncytial infection.

The proposed compounds are manufactured by the reaction between 1-alkylquinoxalinium or 10-methyl-2-phenyl-1,4,4a,5,10,10a-hexahydro-1,3,4-thidiazine [5,6-b] quinoxaline and bornyl or isobornyl ester of acetoacetic acid in the medium of an organic solvent. The synthesis of the proposed compounds is carried out by the following scheme: ##STR7## pps where: R¹ =CH₃, C₂ H₅ ; and R² is bornyl or isobornyl.

For a better understanding of the invention, the following examples of its practical embodiment are given by way of illustration.

EXAMPLE 1

To a mixture of 5 g (0.018 mol) of N-methylquinoxalinium iodide and 5 ml (0.021 mol) of isobornyl acetoacetate in 15 ml of ethyl alcohol added with stirring were 5 ml (0.05 mol) of diethylamine. The starting salt of quinoxaline was dissolved and the temperature of the reaction mixture rose to 40°-50° C. In 15 minutes, the reaction mixture was cooled on ice and passed through a filter to separate colorless crystals. The obtained product, weighing 6.2 g, was isobornyl ester of 2,9-dimethyl-3a,4,9,9a-tetrahydrofuro [2,3-b] quinoxaline-3-carboxylic acid (compound 1a). The yield was 88.6% of theoretical.

A sample of analytical purity was prepared by recrystallization from hexane; the melting point of the product was 144°-145° C. (with decomposition).

Found: %: C 71.6; H 7.9; N 7.3; C₂₃ H₃₀ N₂ O₃. Calculated, %: C 72.2; H 7.9; N 7.3.

¹ H NMR spectrum in deuterochloroform, δ, (ppm): 0.8-1.1 m, 1.4-2.0 m and 4.6-4.9 m (18H, isobornyl residue); 2.10 d (3H, CH₃); 3.07 s (3H, CH₃); 4.96 dd (1H, CH); 5.53 bs (1H, NH), 5.82 d (1H,CH); 6.4-6.9 m (4H, C₆ H₄).

EXAMPLE 2

To a mixture of 5 g (0.018 mol) of N-ethylquinoxalinium iodide and 5 ml (0.021 mol) of isobornyl acetoacetate in 15 ml of ethyl alcohol added with stirring were 5 ml (0.05 mol) of diethylamine. The starting salt of quinoxaline was dissolved and the temperature of the reaction mixture rose to 40°-50° C. In 15 minutes, the reaction mixture was cooled in ice and colorless crystals of isobornyl 2-methyl-9-ethyl-3a,4,9,9a-tetrahydrofuran [2,3-b] quinoxaline-3-carboxylate (compound 1b) were separated on a filter. The yield of the product was 6 g which was 88% of theoretical. The sample of analytical purity was obtained by recrystallization from hexane. The melting point of the product was 132°-133° C. (with decomposition).

Found, %: C 73.3; H 8.2; N 7.2. C₂₄ H₃₂ N₂ O₃. Calculated, %: C 72.9; H 7.9; N 7.1.

¹ H NMR spectrum in deuterochloroform, δ (ppm):0.8-1.1 m. 1.4-20 m and 4.6-4.9 m (18H, isobornyl residue); 1.35 t (3H, CH₃); 2.14 d (3H, CH₃); 3.58 g (2H, CH₂); 4.60 bs (1H, NH); 5.00 dd (1H, CH); 5.96 d (1H, CH); 6.4-6.9 m (4H, C₆ H₄).

EXAMPLE 3

To a mixture of 5 g (0.018 mole) of N-ethylquinoxalinium iodide and 5 ml (0.021 mole) of bornyl acetoacetate in 15 ml of ethyl alcohol added were 5 ml (0.05 mole) of diethylamine. The starting salt was dissolved and the temperature of the reaction mixture rose to 40°-50° C. The mixture was allowed to stand for an hour and the precipitated colorless crystals of bornyl-2-methyl-9-ethyl-3a,4,9,9a-tetrahydrofuro [2,3-b] quinoxaline-3-carboxylate (compound 1c) were separated on the filter. The sample of analytically pure product was obtained by recrystallization from hexane. The yield of the end product was 5.4 g, which was 78% of theoretical. Melting point--121° C. (with decomposition).

Found, C 72.3; H 8.1; N 6.8. C₂₄ H₃₄ N₂ O₃. Calculated, in %: C 72.7; H 8.1; N 7.1.

¹ H NMR spectrum in deuterochloroform, δ, (ppm): 0.8-1.0 m, 1.0-2.5 m and 4.9-5.2 m (18H, bornyl residue); 1.34 t (3H, CH₃); 2.11 d (3H, CH₃); 3.50 m (2H, CH₂); 4.55 b.s (1H, NH); 5.00 dd (1H, CH); 5.98 (1H, CH); 6.5-7.0 m (4H, C₆ H₄).

EXAMPLE 4

To a suspension of 6 g (0.02 mole) of 10-methyl-2-phenyl-1,4,4a,5,10,10a-hexanhydro-1,3,4-thiadiaxine (5,6-b)quinoxaline in 100 ml of ethyl alcohol added were 4 g (0.02 mole) of bornyl acetoatetate. The reaction mixture was heated to 60°-70° C. and allowed to stand at this temperature for 30 minutes. The reaction mixture was then cooled to room temperature and allowed to stand overnight. The precipitated bornyl-3a,5-dimethyl-2-phenyl-3a,4,4a,5,10,10a-hexahydro-1,3,4-thiadiazole [2,3-a] quinoxaline (2,3-d) pyrrole-4-carboxylate (compound 1d) was separated on a filter and recrystallized from ethyl alcohol. The yield of the product was 6.5 g which was 65% of theoretical. The product was a colorless crystalline substance melting at 162°-163° C.

Found, %: C 68.8; H 7.1; N 10.9; S 6.4. C₂₉ H₃₆ N₄ O₂ S. Calculated, %: C 69.0; H 7.2; N 11.1; S 6.4.

¹ H NMR spectrum in deuterochloroform, δ (ppm): 0.8-2.1 m and 4.8-5.0 m (18H, bornyl residue); 2.16 s (3H, CH₃); 3.05 s (3H, CH₃); 3.37 d (1H, CH); 4.30 bs (1H, H); 4.38 dd (1H, CH) 5.02 bs (1H, CH); 6.5-6.9 m (4H, C₆ H₄); 7.2-7.9 m (C₆ H₅).

EXAMPLE 5

To a suspension of 6 g (0.02 mole) of 10-methyl-2-phenyl-1,4,4a,5,10,10a-hexahydro-1,3,4-thiadiazine (5,6-b] quinoxaline in 100 ml of ethyl alcohol added were 4 g (0.02 mole) of isobornyl acetoacetate. The reaction mixture was heated to 60°-70° C. and kept at this temperature for 30 minutes. The mixture was then cooled to room temperature and allowed to stand overnight. The precipitated isobornyl 3a,5-dimethyl-2-phenyl-3a,4,4a,5,10,10a-hexahydro-1,3,4-thiadiazole [2,3-a] quinoxaline [2,3-d]-pyrrole-4-carboxylate (compound 1e) was separated on a filter and recrystallized from ethyl alcohol. The yield of the product was 6.5 g, which was 65% of theoretical. The product was a crystalline substance melting at 167°-168° C.

Found, %: C 69.0; H 6.9; N 11.4; S 6.1. C₂₉ H₃₆ N₄ O₂ S. Calculated, %: C 69.0; H 7.2; N 11.1; S 6.4.

¹ H NMR spectrum in deuterochloroform, δ (ppm): 0.8-2.0 m and 4.5-4.9 m (18H, isobornyl residue); 2.05 s (3H, CH₃); 3.20 d (1H, CH); 2.98 s (3H, CH₃); 4.22 b.s (1H, NH); 4.39 dd (1H, CH); 5.02 b.d (1H, CH); 6.4-6.8 m (4H, C₆ H₄); 7.2-7.8 m (5H), C₆ H₅).

Industrial Applicability

The proposed new compounds, bornyl and isobornyl esters of carboxylic acids of condensed tetrahydroquinoxolines are active against influenza viruses types A, B and C, tick-borne encephalities virus and the virus causing respiratory syncytial infection. Said new compounds can be used in medicine as the active principle of medicinal preparations. 

We claim:
 1. Bornyl and isobornyl esters of carboxylic acids of condensed tetrahydroquinoxalines having the formula ##STR8## wherein: R¹ =CH₃ ; C₂ H₅ ; ##STR9##
 2. Isobornyl ester of 2,9-dimethyl-3a,4,9,9a-tetrahydrofuro 2,3-b quinoxaline-3-carboxylic acid with the following formula ##STR10## as claimed in claim
 1. 